Hard disk drive (HDD) electrical over voltage stress (EOS) systems and methods

ABSTRACT

The present invention relates to a hard disk drive system having overvoltage protection circuits for various types of overvoltage conditions. For example, the system comprises one or more hard disk drive integrated circuit chips residing on a board and a hard disk drive power plug receptacle residing on the board having two different value power supply ports associated therewith. The receptacle is operable to receive a power plug therein, wherein when the power plug is inserted therein in a proper orientation the two different value voltages are properly supplied to the one or more hard disk drive integrated circuit chips, and wherein when the power plug is inserted therein in an improper orientation the two different value voltages are switched with respect to their intended values. The system comprises a reverse power plug orientation protection circuit coupled between the hard disk drive power plug receptacle and at least one of the one or more hard disk drive integrated circuit chips. The protection circuit is operable to detect an improper orientation of the power plug when inserted into the hard disk drive power plug receptacle and reduce a larger of the two different voltage values, thereby preventing an electrical over voltage stress of the at least one hard disk drive integrated circuit chip.

FIELD OF THE INVENTION

[0001] The present invention relates to electronic circuits and, moreparticularly, to a circuit, system, structure and method for reducing orotherwise eliminating electrical over voltage stress (EOS) relatedfailures in hard disk drive (HDD) systems and boards as discussed, andin addition, other memory storage devices such as floppy disk drives,removable hard disk drives, tape drives, CD drives, and DVD drives.

BACKGROUND OF THE INVENTION

[0002] Hard disk drives such as the exemplary drive 10 illustrated inFIG. la include one or a stack of magnetically coated platters 12 thatare used for storing information. The magnetically coated platters 12are mounted together in a stacked position through a spindle 14 whichmay be referred to as a platter stack. The platter stack is typicallyrotated by a motor that is referred to as a spindle motor or a servomotor (not shown). A space is provided between each platter to allow anarm 18 having a read/write head or slider 20 associated therewith to bepositioned on one or both sides of each platter 12 so that informationmay be stored and retrieved. Information is stored on one or both sidesof each platter 12 and is generally organized into sectors, tracks,zones, and cylinders.

[0003] Each of the read/write heads or sliders 20 are mounted to one endof the dedicated suspension arm 18 so that each of the read/write headsmay be positioned as desired. The opposite end of each of the suspensionarms 18 are coupled together at a voice coil motor 16 (VCM) to form oneunit or assembly (often referred to as a head stack assembly) that ispositionable by the voice coil motor. Each of the suspension arms 18 areprovided in a fixed position relative to each other. The voice coilmotor 16 positions all the suspension arms 18 so that the activeread/write head 20 is properly positioned for reading or writinginformation. The read/write heads 20 may move from at least an innerdiameter to an outer diameter of each platter 12 where data is stored.This distance may be referred to as a data stroke.

[0004] Hard disk drives also include a variety of electronic circuitry30 for processing data and for controlling its overall operation asillustrated in FIG. 1b. This electronic circuitry 30 may include apre-amplifier 32, a read channel/write channel circuit 33, a servocontroller 34, a motor control circuit 35, a read-only memory 36 (ROM),a random-access memory 37 (RAM), and a variety of disk control circuitrysuch as an HDD controller 38 or microprocessor to control the operationof the hard disk drive and to properly interface the hard disk drive toa system bus 39, and voltage regulators to supply voltages needed otherthan the ones from the power plug. The pre-amplifier 32 may contain aread pre-amplifier and a write pre-amplifier that is also referred to asa write driver. The pre-amplifier 32 may be implemented in a singleintegrated circuit or in separate integrated circuits such as a readpre-amplifier and a write pre-amplifier or write driver. The diskcontrol circuitry 38 generally includes a separate microprocessor forexecuting instructions stored in memory to control the operation andinterface of the hard disk drive.

[0005] Hard disk drives perform write, read, and servo operations whenstoring and retrieving data. The preamplifier circuit IC is locatedproximate to the arms 18 and a flex 50 is used to couple the signalsback and forth to the remaining circuitry on a printed circuit board(PCB) 52 (see, e.g., FIG. 2b). The PCB 52 contains the remainingcircuitry of FIG. 1b and receives power from a power plug into areceptacle. An exemplary plan view of a plug receptacle or socket isillustrated in FIG. 2c, and designated at reference numeral 54. Thenon-portable PC industry standard socket 54 will comprise a four pinmale type connector for providing supply voltage potentials of 5V, GND,GND and 12V, respectively, to the PCB circuitry.

[0006] The non-portable PC industry standard socket 54 further includestwo 45 degree filled corner tabs 56 which serve as a key to discourageplugging a power plug into the socket 54 in the wrong way, for example,reversing the plug. Unfortunately, in some cases it is still possible toforce the power plug into the socket 54 in an improper orientation ifsufficient force is exerted on the power plug. In such cases, the 5V and12V supply voltages are switched, and circuitry intended to receive 5Vmay receive 12V, which may result in an electrical overvoltage stress(EOS) related circuit failure.

[0007] The 5V only or 3.3V only (no 12V) HDDs for portable PCs use adifferent power plug configuration. In the non-portable use, a 5V HDDwith a different plug configuration may use a socket adapter to thenon-portable industry standard socket 54, and there the possibility ofreverse plugging the socket adapter still exists.

[0008] In addition, the circuitry on the PCB 52 is powered by systempower supplies not located thereon which may not be adequately regulatedor, in some cases, may be defective. Such system conditions may resultin overvoltage conditions at either or both of the 5V and 12V pins,respectively, even when the power plug is properly inserted into thesocket 54. Such overvoltage conditions may also contribute to EOSrelated circuit failures.

SUMMARY OF THE INVENTION

[0009] The present invention relates generally to circuitry forprotecting hard disk drive systems from undesirable voltage conditionsdue to, for example, a reverse power plug condition or an unregulated orotherwise malfunctioning power supply. For example, FIGS. 3.and 5 aretwo different implementations of V5 protection; and FIGS. 6 and 7 aretwo different implementations of V12 protection. Each of theseimplementations provide different levels of protection and V5 and V12protection may be implemented together or independently of one another,as may be desired.

[0010] According to one aspect of the present invention, a hard diskdrive protection system comprises a reverse power plug orientationprotection circuit (see, e.g., FIG. 3). The protection circuit isoperable to detect an improper orientation of a power plug in a powerplug receptacle or socket on a hard disk drive printed circuit board.Upon detection of the improper orientation, the protection circuit isfurther operable to reduce the voltage provided to a circuit board tracewhich is intended to carry a relatively low power supply potential toone or more integrated circuit chips on the board. In the above manner,an overvoltage condition associated with an improperly oriented powerplug is mitigated or otherwise eliminated.

[0011] According to another aspect of the present invention, the reversepower plug orientation circuit comprises a variable resistance circuitwhich is operable to vary a resistance associated therewith as afunction of the power plug orientation. For example, when the power plugis properly inserted into the power plug socket (see, e.g., FIG. 4a),the variable resistance circuit approximates a short circuit withnegligible resistance to substantially pass a supply voltage toassociated hard disk drive components on the printed circuit board.Alternatively, when the power plug is reversed and improperly orientedwithin the power plug socket (see, e.g., FIG. 4b), the variableresistance circuit exhibits a substantial resistance, thereby causing asubstantial voltage drop thereacross and thus reduces a voltage which ispassed to hard disk drive components on the printed circuit board.Consequently, an overvoltage condition associated with a reversed powerplug is mitigated or eliminated altogether.

[0012] According to another aspect of the present invention, thevariable resistance circuit comprises a transistor having a controlterminal coupled to a pin associated with the high supply voltagepotential when the power plug is properly oriented in the socket andanother terminal coupled to a pin associated with a low supply voltagepotential when the power plug is properly oriented. Under normalconditions, the high supply potential activates the transistor causingit to approximate a short circuit. Under adverse conditions when thepower plug is improperly oriented in the power plug, the supplypotentials are switched and the low supply potential is coupled to thetransistor control terminal, thereby decreasing the conduction andincreasing the resistance thereof. Consequently, the high supplypotential present at the transistor is reduced thereacross, thuspreventing the high potential from being transmitted undesirably to oneor more circuit components on the hard disk drive printed circuit board.

[0013] According to still another aspect of the present invention, anovervoltage protection circuit (see, e.g., FIG. 5) is disclosed which isoperable to prevent circuit damage due to reverse plugging or anunregulated or defective 5V power supply in a hard disk drive system.The overvoltage protection circuit comprises a voltage detection circuitwhich is operable to monitor a voltage associated with the low supplyvoltage, and output an activation signal when the voltage associatedtherewith exceeds a predetermined level. The overvoltage protectioncircuit further comprises a voltage reduction circuit operably coupledto the voltage detection circuit, and operable to reduce a value of thelow supply voltage upon receipt of the activation signal from thevoltage detection circuit. Upon activation, the voltage reductioncircuit increases a resistance in a transmission path between the lowvoltage supply and the hard disk drive components, thereby generating avoltage drop there across and reducing the voltage seen at the systemcomponents.

[0014] According to yet another aspect of the present invention, thevoltage detection circuit comprises a zener diode in series with aresistor. When the low supply voltage exceeds a predetermined level, thereverse biased zener diode reaches its zener breakdown voltage andbreaks down, causing current to conduct therethrough. The currentconduction causes a voltage drop to occur across the resistor which isthen used as an activation signal to indicate that an overvoltagecondition has been detected.

[0015] According to still another aspect of the present invention, thevoltage reduction circuit (see, e.g., FIG. 6) comprises a transistorhaving a control terminal coupled to the voltage detection circuit. Upondetection of an overvoltage condition of the 12V power supply, anactivation signal from the voltage detection circuit causes thetransistor to turn on. The transistor is connected to a control terminalof another transistor which is within the transmission path between thesupply voltage being monitored and the hard disk drive components. Whenthe first transistor turns on, the voltage and the control terminal ofthe second transistor in the transmission path goes low, causing it tobecome more resistive. The increased resistance in the transmission pathresults in a reduced voltage at the hard disk drive components, therebyreducing failures associated with electrical overstress (EOS)conditions.

[0016] According to still another aspect of the present invention, anovervoltage protection circuit (see, e.g., FIG. 7) is disclosed which isoperable to prevent circuit damage due to an unregulated or defective12V power supply in a hard disk drive system. The overvoltage protectioncircuit comprises a voltage detection circuit which is operable tomonitor a voltage associated with the high supply voltage, and output anactivation signal when the voltage associated therewith exceeds apredetermined level. The overvoltage protection circuit furthercomprises a voltage reduction circuit operably coupled to the voltagedetection circuit, and operable to reduce a value of the high supplyvoltage upon receipt of the activation signal from the voltage detectioncircuit. Upon activation, the voltage reduction circuit increases aresistance in a transmission path between the high voltage supply andone or more of the hard disk drive components, thereby generating avoltage drop thereacross and reducing the voltage seen at the one ormore system components.

[0017] According to yet another aspect of the present invention, thevoltage reduction circuit uses a pass FET already associated with thehard disk drive system to reduce the voltage when a voltage associatedwith the high voltage supply exceeds a predetermined threshold. When anovervoltage condition is detected, the pass FET becomes less conductingor more resistive, thereby causing a voltage drop thereacross andreducing the value associated with the first supply voltage at thetrace. In addition, a second transistor may be configured in series withthe pass FET such that backgate diodes associated therewith and the passFET are oriented in a back-to-back configuration. Such back-to-backbackgate diodes prevent conduction therethrough under large overvoltageconditions associated with the first supply voltage.

[0018] To the accomplishment of the foregoing and related ends, theinvention comprises the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrativeembodiments of the invention. These embodiments are indicative, however,of but a few of the various ways in which the principles of theinvention may be employed and the present invention is intended toinclude all such embodiments and their equivalents. Other objects,advantages and novel features of the invention will become apparent fromthe following detailed description of the invention when considered inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1a is a perspective view of a prior art disk drive massstorage system;

[0020]FIG. 1b is a schematic diagram illustrating circuitry associatedwith a disk drive mass storage system;

[0021]FIG. 2a is a plan view illustrating a platter having a servo wedgeassociated therewith for use in positioning a read/write head accuratelythereon;

[0022]FIG. 2b is a perspective view of a portion of a disk drive systemillustrating the circuitry associated with the disk drive mass storagesystem;

[0023]FIG. 2c is a plan view of a power plug receptacle or socket havinga key portion for guiding a power plug orientation associated therewith;

[0024]FIG. 3 is a schematic diagram illustrating a reverse plugorientation protection circuit according to one aspect of the presentinvention;

[0025]FIG. 4a is a schematic diagram illustrating the protection circuitof FIG. 3 under normal power plug orientation conditions;

[0026]FIG. 4b is a schematic diagram illustrating the protection circuitof FIG. 3 under adverse conditions where the power plug orientation inthe socket has been reversed;

[0027]FIG. 5 is a schematic diagram illustrating a reverse plugorientation and an overvoltage protection circuit associated with a lowvoltage power supply according to another aspect of the presentinvention;

[0028]FIG. 6 is a schematic diagram illustrating an overvoltagereduction circuit associated with a high voltage power supply accordingto yet another aspect of the present invention; and

[0029]FIG. 7 is a schematic diagram illustrating an overvoltageprotection circuit associated with the high voltage power supplyaccording to still another aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will now be described with respect to theaccompanying drawings in which like numbered elements represent likeparts. The present invention relates to a system and circuitry forpreventing overvoltage conditions on a hard disk drive printed circuitboard.

[0031] Turning now to the figures, FIG. 3 is a combined block level andschematic diagram illustrating an electrical over stress protectionsystem 100 according to one exemplary aspect of the present invention.The system 100 may reside on a hard disk drive printed circuit board(PCB) which includes a hard disk drive power plug receptacle or socket102. According to one exemplary aspect of the present invention, thenon-portable PC industry standard receptacle or socket 102 is a four pinmale type adapter having a pin for a high, first supply voltage value(e.g., about 12V), two pins for circuit ground potential value, and apin for the second, low supply voltage value (e.g., about 5V),respectively. Regulator circuitry 104 may be coupled to a fourth pin 106of the adapter 102 to provide voltage regulation for the other supplyvoltages used within the PCB. A reverse plug orientation protectioncircuit 108 is coupled between the adapter 102 and other hard disk driveboard components (e.g., integrated circuit chips) via one or more supplyvoltage traces 110. The protection circuit, according to one exemplaryaspect of the present invention, is also coupled to the first supplyvoltage value via a first pin 112 of the adapter 102.

[0032] According to an exemplary aspect of the present invention, theprotection circuit 108 is operable to detect an improper orientation ofa power plug when inserted into the receptacle or socket adapter 102 andthen reduce a voltage value at the one or more traces 110 in response tothe detection. For example, the protection circuit 108 may comprise avariable resistor circuit which is operable to adjust a resistance valueassociated therewith based on the orientation of a power plug in thepower plug socket 102. Under normal operating conditions when the powerplug is properly oriented in the socket 102, the variable resistancecircuit exhibits substantially no resistance and approximates a shortcircuit to pass the second supply voltage value to the trace 110 withouta substantial voltage drop thereacross. Under other conditions, however,when the power plug is reversed and plugged into the socket 102 in animproper orientation, the variable resistance circuit exhibits asubstantial resistance, thereby causing a voltage drop thereacross tothereby prevent an undesirable high voltage value form appearing on theone or more traces 110.

[0033] Any type of circuitry which may provide the above functionalitymay be utilized as the protection circuit 108, and such variations arecontemplated as falling within the scope of the present invention. Forexample, according to one aspect of the present invention, theprotection circuit 108 comprises a transistor such as an NMOS transistor114 as illustrated in FIG. 3. In operation, the transistor works asfollows, as illustrated in FIG. 4a and 4 b, respectively. In FIG. 4a,the power plug is inserted into the socket 102 in the proper orientationsuch that the first supply voltage value is provided to the first pin112 (e.g., 12V) and the second supply voltage value is provided to thefourth pin 106 (e.g., 5V), respectively. As seen in FIG. 4a, thisresults in 12V being applied to a control terminal (e.g., a gate) of thetransistor 114, causing it to substantially turn on (e.g., fullconductance). In such a state, the transistor 114 approximates a shortcircuit and almost all of the 5V is passed from the fourth pin 106 ofthe socket 102 to the one or more traces 110.

[0034] Alternatively, when the power plug is inserted into the socket102 in an improper orientation, the first and second supply voltagevalues are switched on the pins 106 and 112, as illustrated in FIG. 4b.That is, the higher voltage (e.g., 12V) now appears on the fourth pin106 and without the help of the transistor 114, would result in a highand potentially damaging voltage appearing on the one or more traces 110which go to various circuit components on the board. However, accordingto the present invention, the transistor 114 now has the lower voltagevalue (e.g., 5V) on its gate terminal, thus causing the conductancethereof to be substantially diminished. That is, the resistanceassociated with the transistor 114 is substantial and therefore asignificant voltage drop (ΔV>0V) will occur across the transistor 114,thereby reducing the voltage on the one or more traces 110 (e.g., ΔV isequal to about 7-8V, thus leaving about 4V at the trace 110.).

[0035] According to another aspect of the present invention, a reverseplug orientation and an overvoltage protection circuit is disclosed, asillustrated in FIG. 5 and designated at reference numeral 150. Theovervoltage protection circuit 150 is operable to reduce the voltage atthe 5V board trace 110 under system conditions when the 5V supplyvoltage exceeds its rated voltage (e.g., increasing substantially above5V) due to, for example, an unregulated or defective 5V supply.According to one exemplary aspect of the present invention, theovervoltage protection circuit 150 comprises a voltage detection circuit152 and a voltage reduction circuit 154, respectively. The voltagedetection circuit 152 is operable to detect a circuit condition in whichthe potential of a 5V supply 156 exceeds a predetermined level, forexample, some value greater than 5V. Upon detection of such a circuitcondition, the voltage detection circuit 152 provides an activationsignal to the voltage reduction circuit 154 which is operable to reducethe voltage associated with the 5V supply 156 at the trace 110 whichsupplies the supply potential to at least one of the various integratedcircuit chips on the hard disk drive printed circuit board.

[0036] In accordance with one exemplary aspect of the present invention,the voltage detection circuit 152 may comprise a zener diode 158 inseries with a resistor 160. In operation, under normal conditions whenthe supply voltage is about 5V, the voltage across the zener diodel 58is reverse biased and the diode 158 is nonconducting. Under anovervoltage condition, however, where the potential of the 5V supply 156exceeds substantially its rated voltage, the zener diode is reversebiased and breaks down (e.g., by setting the zener breakdown voltage atabout the predetermined level which is greater than 5V) and currentconducts therethrough. Based upon the breakdown current, the resistor160 develops a voltage thereacross which serves as an activation signalthat an overvoltage condition has been detected. Although the zenerdiode and resistor combination has been illustrated and described as onetype of voltage detection circuit, other types of circuits may beemployed to provide similar voltage detection functionality and suchalternative circuitry is contemplated as falling within the scope of thepresent invention.

[0037] In accordance with another exemplary aspect of the presentinvention, the voltage reduction circuit 154 may comprise a transistor162 such as an NPN type bipolar transistor having a control terminalcoupled to the voltage detection circuit 152. The voltage reductioncircuit 154 also may include a resistor 164 coupled in series betweenanother, higher value voltage supply 165 (e.g., a 12V supply) and acontrol terminal of another transistor 166, for example, an NMOStransistor. Under normal operating conditions, no activation signal isprovided by the voltage detection circuit 152 to the voltage reductioncircuit 154, and thus the NPN transistor 162 is off. With no currentconduction through transistor 162, the resistor 164 conductssubstantially no current and passes effectively the voltage potential ofthe supply 165 to the gate of the transistor 166. With the gate of thetransistor 166 being high, the transistor 166 is conducting and the 5Vsupply potential is transmitted substantially to the trace(s) 110.

[0038] Under a detected overvoltage condition, however, the voltagedetection circuit 152 provides an activation signal to the base of thetransistor 162, thus turning the transistor 162 on and initiatingcurrent conduction therethrough. As current conducts through the NPNtransistor base 162, a voltage drop occurs across the resistor 164 dueto the current conduction therethrough, thus causing the gate voltage ofthe NMOS transistor 166 to decrease, resulting in decreased currentconduction through the transistor 166. As the NMOS transistor 166becomes more resistive, a voltage drop occurs thereacross, therebydecreasing the voltage supplied by the 5V supply 156 to the trace(s)110. In the above manner, the voltage reduction circuit 152 operates toreduce the voltage at the trace(s) 110 when an overvoltage condition atthe supply 156 is detected.

[0039] Although FIG. 5 illustrates one exemplary voltage reductioncircuit, various types of other circuit components and configurationsmay be employed to provide such functionality and such alternativecircuits are contemplated as falling within the scope of the presentinvention.

[0040] According to yet another aspect of the present invention, anovervoltage protection circuit is disclosed for protecting against anovervoltage condition associated with the high voltage supply (e.g., 12Vsupply), as illustrated in FIG. 6 and designated at reference numeral200. According to one exemplary aspect of the present invention, theovervoltage protection circuit 200 advantageously utilizes a pass FET202 which already exists on the hard disk drive printed circuit board,however, use of such pass FET 202 is not required, and other switchingcomponents or circuits may be utilized and are contemplated as fallingwithin the scope of the present invention.

[0041] The overvoltage reduction circuit 200 in FIG. 6 is operable toreduce the board motor voltage to the servo IC 204, the servo driverFETs 206 and the servo IC motor voltage 208 under system conditions whenthe 12V supply voltage 210 exceeds its rated voltage (e.g., increasingslightly above 12V). According to one exemplary aspect of the presentinvention, the overvoltage protection circuit 200 comprises a voltagedetection circuit 220 and a voltage reduction circuit 222, respectively.The voltage detection circuit 200 is operable to detect a circuitcondition in which the potential of the 12V supply 210 exceeds apredetermined level, for example, some value greater than 12V. Upondetection of such a circuit condition, the voltage detection circuit 220provides an activation signal to the voltage reduction circuit 222 whichis operable to reduce the voltage associated with the 12V supply 210 atthe traces 204, 206 and 208, respectively, which supplies the supplypotential to at least one of the various integrated circuit chips on thehard disk drive printed circuit board.

[0042] In accordance with one exemplary aspect of the present invention,the voltage detection circuit 220 may comprise a zener diode 230 inseries with a resistor 232. In operation, under normal conditions (thesupply 210 properly supplying 12V) the voltage across the zener diode230 is reverse biased and nonconducting. Under an overvoltage condition,however, where the potential of the 12V supply 210 exceeds its ratedvoltage, the zener diode 230 is reverse biased and breaks down (e.g., bysetting the zener breakdown voltage at about the predetermined levelwhich is slightly greater than 12V, for example, about 13V) and currentconducts therethrough. Based upon the breakdown current, the resistor232 develops a voltage thereacross which serves as an activation signalthat an overvoltage condition has been detected. Although the zener andresistor combination has been illustrated and described as one type ofvoltage detection circuit, other types of circuits may be employed toprovide similar voltage detection functionality and any such circuitryis contemplated as falling within the scope of the present invention.

[0043] In accordance with another exemplary aspect of the presentinvention, the voltage reduction circuit 222 may comprise a transistor240 such as an NPN type bipolar transistor having a control terminalcoupled to the voltage detection circuit 220. The voltage reductioncircuit 222 also includes the pass FET 202 having a control terminalcoupled to the NPN transistor 240. The control terminal of the pass FET202 is also coupled to supply disconnect sense circuit 250 which isoperable to detect a system condition where the 12V supply has beendisconnected from the hard disk drive system. Under such conditions, thesense circuit 250 turns off the pass FET 202 to enable the back EMF ofthe motor (not shown) to be used as a power source to park the head intoits proper landing zone via the servo IC 204 in the absence of the 12Vsupply voltage.

[0044] The overvoltage circuit 200 operates in the following exemplarymanner. Under normal operating conditions, no activation signal isprovided by the voltage detection circuit 220 to the voltage reductioncircuit 222, and thus the NPN transistor 240 is off. With no currentconduction through transistor 240, the pass FET 202 remains conductingvia the sense circuit 250 (when the sense circuit 250 does not detect anabsence of the 12V supply). With the gate of the pass FET 202 high, thetransistor 202 is conducting and the 12V supply potential is transmittedsubstantially to the trace(s) 204, 206 and 208, respectively.

[0045] Under a detected overvoltage condition, however, the voltagedetection circuit 220 provides an activation signal to the base of thetransistor 240, thus turning the transistor 240 on and pulling the gateof the pass FET 202 low. As the gate voltage of the pass FET 202decreases, the pass FET 202 becomes more resistive, and a voltage dropoccurs thereacross, thereby decreasing the voltage supplied by the 12Vsupply 210 to the trace(s) 206 and 208. The resistor 281 serves to limitpower dissipation and voltage to other PCB components. In the abovemanner, the voltage reduction circuit 222 operates to reduce the voltageat the trace(s) 206 and 208 when an overvoltage condition at the 12Vsupply 210 is detected. Although FIG. 6 illustrates one exemplaryvoltage reduction circuit, various types of other circuit components andconfigurations may be employed to provide such functionality and suchalternative circuits are contemplated as falling within the scope of thepresent invention.

[0046] In accordance with another aspect of the present invention, theovervoltage protection circuit 200 further comprises a reset circuit 260which is operable to output a reset signal in response to a detected 12Vsupply overvoltage condition. According to one exemplary aspect of thepresent invention, the reset circuit 260 comprises a transistor 262, forexample, an NPN type bipolar transistor having a control terminalcoupled to the voltage detection circuit 220. When the voltage detectioncircuit 220 detects an overvoltage condition associated with the 12Vsupply 210, the activation signal (e.g., the voltage across the resistor232) is output to the reset circuit 260. The activation signal isoperable to turn the transistor 262 on and pull an output 264 thereof,labeled RESETZ down to a circuit ground potential.

[0047] According to an exemplary aspect of the present invention, RESETZis a reset signal that goes to the hard disk drive microprocessor orASIC controller (not shown), depending on the hard disk drive systemconfiguration being employed, which turns off the servo motor and parksthe head in its appropriate landing zone. The microprocessor orcontroller will then re-initiate the hard disk drive system start-upprocess using any one of various well known initialization procedures.Although the above reset circuit 260 is described in conjunction with atransistor 262, other circuits providing similar functionality may beemployed and such alternatives are contemplated as falling within thescope of the present invention.

[0048] In the above example, the circuit 200 operates well when the 12Vsupply 210 experiences an overvoltage condition which is notsubstantially greater than the rated supply voltage of about 12V. Incases where the 12V supply potential greatly exceeds its rated voltage(e.g., about 30V), the circuit 200 has some potential limitations. Forexample, the diode (not shown) which is implicit in the pass FET 202(the backgate diode) will tend to conduct when the voltage from thesupply 210 is greater than the board motor voltage VM 206. Consequently,the voltage at the traces 206 and 208 will get clamped at about abackgate diode drop (e.g., about 1V) below the supply potential 210. Forsupply potentials not substantially greater than 12V (e.g., about13-15V) such protection may be acceptable, however, for supply voltagessubstantially greater, large potentially undesirable voltages may stillappear on the traces 206 and 208, respectively.

[0049] According to still another aspect of the present invention, acircuit for protecting against substantial overvoltage conditions on thehigh voltage supply is disclosed in FIG. 7, and designated at referencenumeral 280. The overvoltage protection circuit 280 is similar in manyrespects to the circuit 200 of FIG. 6, however, the circuit 280 of FIG.7 has a voltage reduction circuit 290 that differs from the voltageprotection circuit 222 of FIG. 6. The voltage protection circuit 290 hasa second transistor 292, for example, an NMOS transistor, in series withthe pass FET 202 such that their backgate diodes are coupled together ina back-to-back series fashion (e.g., cathode to cathode). In the abovemanner, when the 12V supply voltage 210 increases substantially aboveits rated voltage, although the backgate diode associated with the passFET 202 becomes forward biased, the second backgate diode associatedwith the transistor 292 is reverse biased and no current conductstherethrough. Consequently, a substantial portion of the voltage isdropped across the reverse biased backgate diode of transistor 292, thusprotecting the traces 206 and 208 from experiencing a potentiallyundesirable high voltage thereat.

[0050] Although the invention has been shown and described with respectto a certain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described components (assemblies, devices,circuits, etc.), the terms (including a reference to a “means”) used todescribe such components are intended to correspond, unless otherwiseindicated, to any component which performs the specified function of thedescribed component (i.e., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several embodiments,such feature may be combined with one or more other features of theother embodiments as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the term“includes” is used in either the detailed description and the claims,such term is intended to be inclusive in a manner similar to the term“comprising.”

What is claimed is:
 1. A memory storage device circuit board such as ahard disk drive circuit board, comprising: one or more hard disk driveintegrated circuit chips residing on the board; a hard disk drive powerplug receptacle residing on the board having two different value powersupply ports associated therewith and operable to receive a power plugtherein, wherein when the power plug is inserted therein in a properorientation the two different value voltages are properly supplied tothe one or more hard disk drive integrated circuit chips, and whereinwhen the power plug is inserted therein in an improper orientation thetwo different value voltages are switched with respect to their intendedvalues; and a reverse power plug orientation protection circuit coupledbetween the hard disk drive power plug receptacle and at least one ofthe one or more hard disk drive integrated circuit chips, wherein thereverse power plug is operable to detect an improper orientation of thepower plug when inserted into the hard disk drive power plug receptacleand reduce a larger of the two different voltage values, therebypreventing an electrical over voltage stress of the at least one harddisk drive integrated circuit chip.
 2. The memory storage device circuitboard of claim 1, wherein the reverse power plug orientation protectioncircuit comprises a variable resistor circuit having a first terminalcoupled to a portion of the power plug receptacle associated with alower of the two different voltage values when the power plug isproperly inserted therein, and having a second terminal coupled to atrace on the board for transmitting the lower voltage value to at leastone of the hard disk drive integrated circuit chips, and wherein whenthe power plug is inserted properly into the power plug receptacle, thevariable resistor approximates a short circuit, thereby substantiallytransmitting the lower voltage value to the at least one integratedcircuit chip, and wherein when the power plug is inserted in an improperorientation, the variable resistor is substantially resistive, causingthe larger voltage value to experience a voltage drop thereacross,thereby reducing a voltage value at the trace and preventing anelectrical over voltage stress of the at least one hard disk driveintegrated circuit chip.
 3. The memory storage device circuit board ofclaim 2, wherein a resistance of the variable resistor circuit iscontrolled by a voltage value at another portion of the power plugreceptacle associated with the larger of the two different voltagevalues when the power plug is properly inserted therein.
 4. The memorystorage device circuit board of claim 2, wherein the variable resistorcircuit comprises a transistor having a control terminal coupled toanother portion of the power plug receptacle associated with the largerof the two different voltage values when the power plug is properlyinserted therein.
 5. The memory storage device circuit board of claim 4,wherein the transistor comprises an NMOS transistor, and wherein thecontrol terminal comprises a gate terminal thereof.
 6. The memorystorage device circuit board of claim 1, wherein the hard disk driverpower plug receptacle comprises a four pin adapter, wherein a first pinis intended to accommodate a first supply voltage value, a second andthird pin are intended to accommodate a circuit ground potential value,and a fourth pin is intended to accommodate a second supply voltagevalue, wherein the first supply voltage value is greater than the secondsupply voltage value.
 7. The memory storage device circuit board ofclaim 6, wherein the reverse power plug orientation protection circuitcomprises: a sensing circuit operable to detect an improper orientationof the power plug in the power plug receptacle; and a voltage reductioncircuit associated with the fourth pin of the four pin adapter, andoperable to reduce a voltage associated with the fourth pin when thesensing circuit detects the improper power plug orientation.
 8. Thememory storage device circuit board of claim 6, wherein the reversepower plug orientation protection circuit comprises a variableresistance circuit, and is operable to exhibit substantially noresistance when the power plug is inserted into the four pin adapter inthe proper orientation, and wherein the variable resistance circuit isoperable to exhibit a substantial resistance when the power plug isinserted into the four pin adapter in the improper orientation.
 9. Thememory storage device circuit board of claim 8, wherein the variableresistance circuit comprises a transistor having a control terminalcoupled to the first pin of the four pin adapter, wherein when the powerplug is inserted into the four pin adapter in the proper orientation,the transistor is substantially conducting and behaving approximately asa short circuit, and wherein when the power plug is inserted into thefour pin adapter in the improper orientation, the transistor ispartially conducting and exhibits a substantial resistance and thereforea substantial voltage drop thereacross.
 10. An overvoltage protectioncircuit, comprising: one or more hard disk drive integrated circuitchips residing on a board; a first voltage supply potential forsupplying power to at least one of the one or more hard disk driveintegrated circuit chips; a second voltage supply potential having anintended value which is less than the first voltage supply potential,the second voltage supply potential for supplying power to at least oneof the one or more hard disk drive integrated circuit chips; a voltagedetection circuit operable to detect a value of the second voltagesupply potential; and a voltage reduction circuit operably coupled tothe voltage detection circuit, wherein the voltage detection circuit isoperable to activate the voltage reduction circuit when the secondvoltage supply potential exceeds a predetermined threshold, and whereinthe voltage reduction circuit is operable to reduce a value of thesecond supply potential when activated by the voltage detection circuit.11. The overvoltage protection circuit of claim 10, wherein the voltagereduction circuit is further operably coupled to the first voltagesupply potential.
 12. The overvoltage protection circuit of claim 10,wherein the voltage detection circuit comprises a zener diode which isreverse biased and conducts substantially no current when the secondvoltage supply potential is less than the predetermined threshold. 13.The overvoltage protection circuit of claim 10, wherein the voltagedetection circuit further comprises a resistor coupled in series withthe zener diode, wherein when the zener diode has a reverse bias voltagethereacross which exceeds the predetermined threshold, the zener diodebreaks down and conducts current therethrough, thereby generating avoltage across the resistor, and wherein when the voltage across theresistor exceeds a predetermined level, the voltage activates thevoltage reduction circuit.
 14. The overvoltage protection circuit ofclaim 13, further comprising a first transistor coupled between thesecond voltage supply potential and a trace which transmits the secondvoltage supply potential to at least one of the one or more hard diskdrive integrated circuit chips, and wherein the first transistor has acontrol terminal coupled to the first voltage supply potential, andwherein the voltage reduction circuit comprises a second transistorcoupled to the control terminal of the first transistor and having acontrol terminal coupled to the resistor of the voltage detectioncircuit, wherein when the voltage across the resistor in the voltagedetection circuit exceeds the predetermined level, the second transistorturns on and lowers a voltage of the control terminal of the firsttransistor, thereby reducing a conduction of the first transistor andreducing a voltage value provided by the second voltage supply potentialto the trace.
 15. An overvoltage protection circuit for a hard diskdrive circuit board, comprising: one or more hard disk drive integratedcircuit chips residing on the board; a first voltage supply potentialfor supplying power to at least one of the hard disk drive integratedcircuit chips; a second voltage supply potential for supplying power toat least one of the hard disk drive integrated circuit chips, whereinthe second voltage supply potential has an intended value which is lessthan the first voltage supply potential; a first transistor coupledbetween the second voltage supply potential and a trace for transmittingthe second voltage supply potential to the at least one hard disk driveintegrated circuit chip, and a control terminal coupled to the firstvoltage supply potential through a first resistor, wherein when thefirst transistor is substantially conducting, the second voltage supplypotential is transmitted substantially to the trace, and wherein whenthe first transistor is not conducting substantially, a substantialvoltage drop exists thereacross and a voltage potential transmitted tothe trace is less than the second voltage supply potential; a zenerdiode coupled to the first transistor and operable to be reverse biasedand nonconducting when a value of the second voltage supply potential isless than a predetermined level, and wherein the zener diode is operableto break down and conduct current therethrough when the value of thesecond voltage supply potential is greater than or equal to thepredetermined level; a second resistor coupled in series with the zenerdiode and operable to exhibit a voltage thereacross when the zener diodeis conducting current; and a second transistor coupled between thecontrol terminal of the first transistor and one terminal of the secondresistor, and a control terminal coupled to the other terminal of thesecond resistor, and wherein when the zener diode conducts current dueto the second voltage supply potential exceeding the predeterminedlevel, a voltage develops across the second resistor and causes thesecond transistor to conduct, and wherein the conduction of the secondtransistor causes a conduction of the first transistor to be reduced,thereby reducing the voltage at the trace.
 16. An overvoltage protectioncircuit, comprising: one or more hard disk .drive integrated circuitchips residing on a board; a first voltage supply potential forsupplying power to at least one of the one or more hard disk driveintegrated circuit chips; a second voltage supply potential having anintended value which is less than the first voltage supply potential,the second voltage supply potential for supplying power to at least oneof the one or more hard disk drive integrated circuit chips; a voltagedetection circuit operable to detect a value of the first voltage supplypotential; and a voltage reduction circuit operably coupled to thevoltage detection circuit, wherein the voltage detection circuit isoperable to activate the voltage reduction circuit when the secondvoltage supply potential exceeds a predetermined threshold, and whereinthe voltage reduction circuit is operable to reduce a value of the firstsupply potential when activated by the voltage detection circuit. 17.The overvoltage protection circuit of claim 16, wherein the voltagedetection circuit comprises a zener diode which is reverse biased andconducts substantially no current when the first voltage supplypotential is less than the predetermined threshold.
 18. The overvoltageprotection circuit of claim 16, wherein the voltage detection circuitfurther comprises a resistor coupled in series with the zener diode,wherein when the zener diode has a reverse bias voltage thereacrosswhich exceeds the predetermined threshold, the zener diode breaks downand conducts current therethrough, thereby generating a voltage acrossthe resistor, and wherein when the voltage across the resistor exceeds apredetermined level, the voltage activates the voltage reductioncircuit.
 19. The overvoltage protection circuit of claim 18, wherein thevoltage reduction circuit comprises: a first transistor coupled betweenthe first voltage supply potential and a trace which transmits the firstvoltage supply potential to at least one of the one or more hard diskdrive integrated circuit chips; and a second transistor coupled to acontrol terminal of the first transistor and having a control terminalcoupled to the resistor of the voltage detection circuit, . wherein whenthe voltage across the resistor in the voltage detection circuit exceedsthe predetermined level, the second transistor turns on and lowers avoltage of the control terminal of the first transistor, therebyreducing a conduction of the first transistor and reducing a voltagevalue provided by the first voltage supply potential to the trace. 20.The overvoltage protection circuit of claim 16, further comprising areset circuit coupled to the voltage detection circuit, wherein thereset circuit is operable to activate a reset signal to a controllercircuit associated with the board to reset the one or more circuitcomponents on the board when voltage detection circuit detects a firstvoltage supply potential which exceeds the predetermined threshold. 21.The overvoltage protection circuit of claim 20, wherein the resetcircuit comprises a transistor having a control terminal coupled to thevoltage detection circuit, wherein an activation of the voltagedetection circuit due to an overvoltage detection causes the transistorto change conduction states, thereby changing a voltage state on anoutput of the transistor which serves as the reset signal.
 22. Theovervoltage protection circuit of claim 16, wherein the voltagereduction circuit comprises: a first transistor having a backgate diodeassociated therewith; and a second transistor having a backgate diodeassociated therewith, wherein the first and second transistor arecoupled together in series in such a manner that the backgate diodes areoriented with respect to one another in a back-to-back fashion, therebypreventing conduction therethrough under overvoltage conditions when thefirst and second transistors are biased in a substantially resistivecondition based on an activation signal from the voltage detectioncircuit.
 23. The overvoltage protection circuit of claim 22, wherein aback-to-back orientation of the backgate diodes comprises aconfiguration where a cathode terminal of the backgate diodes arecoupled together or a configuration where an anode terminal of thebackgate diodes are coupled together.
 24. An overvoltage protectioncircuit for a hard disk drive circuit board, comprising: one or morehard disk drive integrated circuit chips residing on the board; a firstvoltage supply potential for supplying power to at least one of the harddisk drive integrated circuit chips; a second voltage supply potentialfor supplying power to at least one of the hard disk drive integratedcircuit chips, wherein the second voltage supply potential has anintended value which is less than the first voltage supply potential; afirst transistor coupled between the first voltage supply potential anda trace for transmitting the first voltage supply potential to the atleast one hard disk drive integrated circuit chip, wherein when thefirst transistor is substantially conducting, the first voltage supplypotential is transmitted substantially to the trace, and wherein whenthe first transistor is not conducting substantially, a substantialvoltage drop exists thereacross and a voltage potential transmitted tothe trace is less than the first voltage supply potential; a zener diodecoupled to the first transistor and operable to be reverse biased andnonconducting when a value of the first voltage supply potential is lessthan a predetermined level, and wherein the zener diode is operable tobreak down and conduct. current therethrough when the value of the firstvoltage supply potential is greater than or equal to the predeterminedlevel; a second resistor coupled in- series with the zener diode andoperable to exhibit a voltage thereacross when the zener diode isconducting current; and a second transistor coupled between the controlterminal of the first transistor and one terminal of the secondresistor, and a control terminal coupled to the other terminal of thesecond resistor, wherein when the zener diode conducts current due tothe first voltage supply potential exceeding the predetermined level, avoltage develops across the second resistor and causes the secondtransistor to conduct, and wherein the conduction of the secondtransistor causes a conduction of the first transistor to be reduced,thereby reducing the voltage at the trace.
 25. The overvoltageprotection circuit of claim 24, further comprising a third transistorcoupled in series between the first transistor and the zener diode, andwherein the first and third transistors have backgate diodes associatedtherewith in which the backgate diodes are oriented in a back-to-backconfiguration, thereby preventing conduction therethrough when the firstand third transistors are biased in a substantially resistive conditionbased on an activation of the second transistor when an overvoltagecondition is detected.